Object Constraint Language

in Together

Dan Massey

Y&L Consulting

Picking up From Logicians

Follows 3242 presentation to go in depth on OCL and using OCL in tools

The preconference tutorial used the slides from session 3242 as the first third of the presentation.

OCL Topics

OCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

OCL Topics

OCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

OCL is

Strongly typed declarative language

Small set of built-in types, including collections

User-defined types and operators

OCL Basic Types

Boolean true or false

Integer theoretically unlimited natural numbers, subtype of Real

Real mathematical Real, no specific

implementation implied

String ‘sequence of characters’

Boolean Operations

a : Boolean b : Boolean

a and b a or b a xor b

not a a = b a <> b

a implies b

implies constraint:

if a is true then b must be true

Numeric Operators

Comparison

= equals <> not equals

< less > more

<= less or equal >= more or equal

Math

+ addition - subtraction

* multiplication / division

Every Type in OCL is an Object

a : Integer b:Integer

a.mod(b) a.div(b)

a.abs() a.max(b)

a.min(b) a.round()

a.floor()

Operators are just infix notation operations.

String Operations

a : String b : String

a = b a <> b

a.concat(b) a.size()

a.toLower() a.toUpper()

a.subString(1, 3)

Operations return new Strings.

OCL Conditional

OCL provides one conditional construct:

if <Boolean expression>

then <expression>

else <expression>

endif

No “elseif” or “switch”/“case”

OCL Operation Precedence

Grouping ()Path resolution ::Message notation . -> also ^ ^^Unary - notMultiplication/Division * /Addition/Subtraction + -Comparison < > <= >= <> =Logical and or xorLogical implication implies

User-Defined Types

Classes, Interfaces, etc. defined in the model

Users may overload infix and unary operators:

Multiply Money by a Real

Add two Distance values

OCL Collections

Refreshing our memories, we have:

Collection

Bag Sequence

Set OrderedSet

OCL allows you to treat any instance like a collection. You can ask if a single attribute is empty.

Collections must by Typed

Set(Bid)

Bag(String)

Like generics in Java or templates in C++.

Collections Literals

Use curly brackets around comma lists to specify Collection literals.

Bag {‘sock’, ‘sock’, ‘shirt’, ‘sweater’, ‘sock’}

Sequence {‘abe’, ‘bob’, ‘bob’, ‘tim’, ‘zak’}

Set {16.0, 2.0, 64.0, 8.0, 128.0, 3.5}

OrderedSet {1, 2, 4, 8, 16, 32, 64, 128}

You can also specify Collections of Collections.

Basic Collections Operations

a : Set(String) b : String c : Set(String)

a = c a <> c

a->size() a->count(b)

a->excludes(b) a->excludesAll(c)a->includes(b) a->includesAll(c)a->isEmpty() a->notEmpty()a->sum() -- contents are of type supporting +

More Collections Operations

OCL supports a wide range of Collection operations that vary by Collection type.

first(), last(), at(i : Integer), etc. for {ordered} collections

union(), -, asSet(), including(), symmetricDifference(collection : Collection) are a sample

Flatten

Recursively adds the members of nested collections to a single collection.

context MyTypedef: a : Set(Set(Integer)) =

Set {Set{1, 2, 3}, Set{3, 4, 5}, Set{4, 5, 6}}

a->flatten() = Set{2, 3, 1, 5, 4, 6} -- no order

Collection Loops

OCL supports an iterate() operation for Collections. On top of that idea, OCL provides a set of Collection operations that accept expression.

Examples:

any(expression) exists(expression)

collect(expression) one(expression)

select(expression) reject(expression)

Other OCL Types

OclAny the root Type

OclVoidthe “null” Type “undefined”

OclType a type, like “Class” in Java

OCL provides operations for type identification.

Tuple group of named values

Tuple {name : String = ‘Dan’, role : Role = Role::Speaker}

OCL Topics

OCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

Liquid Lemons Domain

LL Invariantscontext Sale-- a Sale has one or more itemsinv numberOfSaleItems : items->size() > 1

-- a Sale's subtotal may not be less than zeroinv subtotalGreaterThanZero : subtotal().amount >

0.0 and subtotal().currency = Currency::USDollars

LL Pre and Postcontext LiquidLemons::addLemonade(flavor :

Flavor, size : DrinkSize)pre activeSale : currentSale->size() = 1pre mustHaveFlavor : not flavor.oclIsUndefined()pre mustSpecifySize : not size.oclIsUndefined()post newLemonade :

currentLemonade->size() = 1

LL Query

Collections Queries

context ItemAnalyzer::averagePrice() : Moneybody: items.basePrice()->sum() /

items.basePrice()->size()

context ItemAnalyzer::uniqueModDescriptions() : Set(String)

body: items.modDescriptions() ->flatten()->asSet()

Composite QueriesUse small methods with single responsibilities to build up

larger functions.

-- the total we want is subtotal plus taxcontext Sale::total() : Moneybody: subtotal() + tax()

-- tax is the subtotal times the local tax ratecontext Sale::tax() : Moneybody: subtotal() * Tax::localRate

Composite Queries Cont.context Sale::subtotal() : Moneybody: items.price()->sum()

context LineItem::price() : Moneybody: basePrice() + modsPrice()

context LineItem::modsPrice() : Moneybody: modifiers.price()->sum()

Don’t Do Thiscontext LineItem::basePrice() : Moneybody: if size = DrinkSize::Small then if flavor = Flavor::Regular then Money::newInstance(1.23, Currency::USDollars) else Money::newInstance(1.73, Currency::USDollars) endif else if flavor = Flavor::Regular then Money::newInstance(2.43, Currency::USDollars) else Money::newInstance(3.13, Currency::USDollars) endif endif

Use Polymorphism

Little policy classes are an extension of the little operations idea. Smaller rules are easier to read.

context LargeRegularLemonade::basePrice() : Moneybody: Money::newInstance(2.43, Currency::USDollars)

context SmallFlavoredLemonade::basePrice() : Moneybody: Money::newInstance(1.72, Currency::USDollars)

OCL Topics

OCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

Where Does the OCL Go?

Use the named property fields and boxes.

Shows up in generated docs and XMI export.

Not visible in diagrams.

OCL Notes

Attach notes containing OCL to correct contexts.

OCL is visible in the diagrams.

Potential to clutter the model.

Together Designer

Syntax checked OCL in “Constraint Notes” that establish context.

Now in field test.

OCL Topics

OCL Basics

The LiquidLemons Example

OCL in Together

Team Modeling Exercise

Domain Options

Tic-Tac-Toe

Ants

Electronic Voting

Poem

Golf

Turtle Logo

Dog Kennel